Measure the Crispix or Chex cereal into a large bowl or lidded container and set aside.

In a microwave-safe bowl, combine the butter, peanut butter, and chocolate chips. Microwave on high for 1 minute, then stir. Continue microwaving in 1-minute intervals, stirring between each round, until the mixture is fully melted and smooth (about 2–3 minutes total).

Stir in the vanilla extract until well combined.

Carefully pour the warm chocolate peanut butter mixture over the cereal. Gently stir with a spatula or wooden spoon until evenly coated.

Add the powdered sugar in batches, mixing lightly after each addition. Cover the bowl with plastic wrap or secure the lid on your container and shake until all pieces are well coated.

Spread the puppy chow onto a parchment-lined baking sheet to cool. Serve once set—or enjoy immediately.